1. Field of the Invention
The present invention relates to an ultrasonic treatment appliance for incising, resecting, or coagulating a clamped region by propagating ultrasonic vibrations to a clamping portion that clamps a living tissue.
2. Description of the Related Art
In the past, an ultrasonic therapeutic appliance has been used to resect the prostate, crush calculi, or resect the liver. The ultrasonic therapeutic appliance is constructed by concatenating an ultrasonic transducer, horn, and vibration propagation member. Ultrasonic vibrations generated by the ultrasonic transducer are amplified mechanically by the horn, and transmitted to the vibration propagation member. The distal end of the ultrasonic propagation member and its surroundings are brought into contact with a living tissue of a lesion. The ultrasonic therapeutic appliance falls into an ultrasonic suction appliance having a pipe-like probe for emulsifying a tissue by utilizing ultrasonic vibrations, sucking a resultant tissue, and thus crushing and removing a lesion, and an ultrasonic coagulation/incision appliance having a scissors-like probe for coagulating or incising a tissue by utilizing heat derived from ultrasonic vibrations.
For example, the specification of U.S. Pat. No. 3,636,943 has disclosed a procedure of causing the tip of a probe to dissipate heat of a high temperature by applying ultrasonic vibrations to the probe serving as an ultrasonic treatment appliance, then resecting a living tissue and coagulating a bleeding region immediately at the same time, and thus effectively resecting a living tissue without causing bleeding. Japanese Unexamined Patent Publication No. 1-232948 has disclosed a treatment system configured to efficiently resect a living tissue by applying ultrasonic vibrations to a resection clamp. In the case of the treatment systems disclosed in the specification of the U.S. Pat. No. 3,636,943 and in the Japanese Unexamined Patent Publication No. 1-232948, the whole of a contact part that comes into contact with a living tissue during ultrasonic treatment is made of a metallic material.
The specification of U.S. Pat. No. 5,322,055 has presented an ultrasonic treatment appliance having a clamping member formed above the tip of a probe serving as a vibration propagation member, and conducting ultrasonic treatment while clamping and immobilizing a living tissue using the distal part of the probe and the clamping member. In this kind of ultrasonic treatment appliance, a soft contact member made of a plastic material is placed on a contact surface of a clamping member that comes into contact with a living tissue. The employment of the soft contact member prevents a noise from occurring when metallic clamping members meet during ultrasonic treatment.
The sharpness of the ultrasonic treatment appliance in resecting a living tissue is known to vary depending on the frequency of ultrasonic vibrations. For example, when a relatively low frequency is selected as a frequency to be set in an ultrasonic transducer, a distance of the position of a node in a probe which acts as a fulcrum of a clamping member for clamping a living tissue from the tip of the probe acting as a working point of the clamping member gets larger. The probe is therefore likely to deflect when a load is applied by the clamping member. When the clamping member is used to clamp a living tissue, force exerted to clamp the living tissue weakens. The living tissue cannot therefore be clamped reliably and may come off from the clamping member. As a result, the work of resecting the living tissue becomes hard to do. This poses a problem of deteriorated workability.
As described in the specification of the U.S. Pat. No. 5,322,055, when a clamping member made of a resin material such as so-called Teflon is employed, when the clamping member clamping a living tissue is highly heated by propagated ultrasonic vibrations, the clamping member may be deformed due to the heat. If the clamping member is thermally deformed, force exerted to clamp a living tissue weakens. Consequently, the living tissue cannot be clamped reliably and may come off from the clamping member. As a result, the work of resecting the living tissue becomes hard to do. This poses a problem of deteriorated workability.
Furthermore, the width of a clamping member for clamping a living tissue in cooperation with the distal part of an ultrasonic probe must, in principle, be considerably small so that the clamped state can be readily discerned by an endoscope. If the clamping member is made of a resin material such as so-called Teflon and is thin, the resin clamping member is liable to be damaged, that is, deformed, melted to be burnt, or worn out because of heat generated during ultrasonic treatment and clamping force. Even if the clamping member is made thick, the resin material is inferior in durability to metals or the like from both thermal and mechanical viewpoints. Even if the thickness of a clamping member made of a resin material were increased, durability would not drastically improve.
As mentioned above, a clamping member made of a resin material is inferior in durability to any metallic clamping member from both thermal and mechanical viewpoints. This poses a problem that ultrasonic treatment cannot be conducted with high power and treatment efficiency is hard to improve. In an effort to solve this problem, it is conceivable to produce a clamping member using a metallic member. In this case, the problem of the thermal and mechanical inferiorities of the clamping member made of a resin material can be solved but a problem described below arises newly.
The instant a living tissue clamped by the distal part of an ultrasonic probe is incised perfectly, the vibrating distal part of the probe comes into contact with the surface of a clamping member formed with a metallic member. This results in a violent loud mechanical sound. This phenomenon is presumably attributable to the fact that since the probe for propagating ultrasonic vibrations is elongated, vibrations including ultrasonic vibrations as well as complex vibrations such as rolling occur in the distal part, and as a result, a hit sound occurs at the distal end of the metallic clamping member.
Moreover, when the ultrasonic suction appliance is in use, the vibration propagation member may receive an extraneous force oriented in a lateral direction when meeting an object or the like. In this case, the probe that is the vibration propagation member meets a coaxial sheath fitted on the outer circumference of the probe with a certain distance between them. Consequently, the meeting portion of the vibration propagation member is worn out. Otherwise, in the case of the ultrasonic coagulation/incision appliance, friction occurs between the vibration propagation member structured as one of blades of scissors and a clamping member structured as the other blade thereof and designed not to vibrate ultrasonically. The friction results in abrasion.
As a method of preventing the abrasion that results from friction, Japanese Unexamined Patent Publication No. 5-95955 has disclosed a technology for hardening the surface of the vibration propagation member. According to the technology, the surface of a titanium alloy normally made into the vibration propagation member is coated by performing physical-vapor deposition (PVD) such as ion plating or chemical-vapor deposition (CVD).
According to the CVD, coating is carried out under a high-temperature environment. A coating is attached closely to a base material. However, the phase of the base material is affected. This causes the properties of the titanium alloy that is the base material to change. The performance of transmission of ultrasonic waves is reportedly affected adversely. For this reason, an actually adopted coating method is the PVD.
However, if the PVD were adopted for coating, a coating layer would be a film whose thickness is limited to about 3 .mu.m cost-wise. When the vibration propagation member and sheath meet for a long period of time as mentioned previously, the coating of the thin film would readily be worn away and the base material would be exposed. Consequently, an internal stress and bending stress stemming from applied ultrasonic vibrations are concentrated on the abraded portion of the vibration propagation member. If ultrasonic vibrations are kept applied to the portion, the vibration propagation member comes to a limit of endurance against a fatigue failure. An initial crack develops in the abraded portion, thus leading to the fatigue failure. Although the coating is as thin as 3 .mu.m in thickness, the Vickers hardness of the coating is approximately 1200. By contrast, the Vickers hardness of the titanium alloy that is the base material is approximately 600. For example, when a strong impact is imposed on the surface of the coating on the vibration propagation member, even if the coating is free from any damage, the impact is imposed on the base material. Consequently, the base material may crack. In this case, the base material under the coating layer a flaw may be flawed, and stresses may be concentrated on the flaw during transmission of ultrasonic waves. This brings about a factor of causing an initial crack leading to a breakage.
Moreover, an ultrasonic treatment appliance may be used to coagulate or cut away a large region of a tissue that is relatively hard to cut away, for example, the liver or duodenum. For this purpose, a large clamping force is needed.
In this case, a large bending stress is induced in a probe. The bending stress causes the probe to warp in a direction in which the claming member is closed, that is, a direction opposite to a direction in which the clamping member is located. Generally, the clamping member is designed to press the whole probe with the same load. When an object is clamped, a uniform load is applied to the probe.
At this time, the bending stress induced in the probe depends greatly on the sectional shape of the clamping portion of the probe, that is, the section modulus thereof.
Currently, as presented in the U.S. Pat. No. 5,322,055, the cross sectional shape of the clamping portion of a probe is fixed to a certain shape in the direction of the length thereof.
Now, actual treatment will be discussed.
As the diameter of a probe is smaller, a field of view provided near the tip of the probe is wider. This permits delicate treating manipulation. However, since the probe is shaped so that the section modulus is small for a normal stress in the probe. The probe therefore warps.
Moreover, the outer diameter of the insertion unit of the aforesaid existing handpiece is approximately 10 mm. If the handpiece is designed compactly to have an outer diameter of 5 mm or 3 mm, the sectional area of the probe must be made smaller than the existing one. At this time, the probe exhibits a small section modulus for a normal stress required for coagulating or cutting away a tissue.
Assume that a probe has a shape like the existing shape enabling the probe to exhibit a constant section modulus, which is smaller than a certain value, over the distal part of the probe. In this case, when a quantity of clamping force that is a normal stress increases, the probe may warp.
When the probe cooperates with the clamping member warps in clamping a tissue, if the probe warps, the probe and clamping member do not fully mesh with each other. In other words, the roots of the probe and clamping member have such a positional relationship that a tissue is attached closely to the roots and cannot therefore be coagulated or cut away. The tips thereof have such a positional relationship that they are spaced enough to coagulate or cut away a tissue. This leads to a problem that the ability to resect a tissue deteriorates.
Moreover, an operator may manipulate the ultrasonic treatment appliance to limit the movements of the clamping member in an effort to reduce a quantity of clamping force. The operator intends to prevent the probe from warping to have the positional relationship that disables coagulation or cutting. As a result, the quantity of clamping force becomes too small. This poses the problem of the deteriorated ability to resect a tissue.
Furthermore, there is another problem that a probe, or especially, the upper side of the probe is prone to flaws.
For example, an incorrect treatment appliance may be grabbed by mistake during ultrasonic oscillation within an actual surgical procedure. In this case, it is unavoidable that the upper side of the probe is flawed even slightly.
Moreover, a burnt tissue sticking to the upper side of the probe may be washed away during cleaning after use. When the upper side of the probe is scrubbed using a sharp cleaning tool, the probe may be flawed.
Moreover, similarly to an ultrasonic treatment appliance disclosed in the Japanese Unexamined Patent Publication No. 10-127654, some ultrasonic treatment appliances have a metallic probe mated with a clamping member. Every time the probe is vibrated ultrasonically, the probe rubs against the clamping member. The probe may then be flawed.
It can be said that the aforesaid ultrasonic treatment appliances are structured so that the upper side of each probe and its surroundings are prone to a flaw, that is, a small crack.
Assume that a living tissue is clamped and the probe is vibrated ultrasonically with a small crack created on the upper side of the probe. A stress distribution is a compound of stresses induced by ultrasonically vibrating the probe (in this case, generally, a maximal stress is observed at nodes of ultrasonic vibrations and a minimal stress is observed at antinodes thereof), and a bending stress induced in the probe due to clamping. The stresses act on the flaw on the upper side of the probe. At this time, the bending stress induced by claming a tissue works as a load stress causing the flaw on the upper side of the probe to expand. In this state, when the probe is vibrated repeatedly, a fatigue crack may develop with the flaw as an origin.